NORTHEASTERN FOREST EXPERIMENT STATION 

Upper Darby , Pennsylvania 

No. 83 

1958 

GROWTH OF WHITE PINE AND 

RED SPRUCE TREES AFTER PRUNING 

Are pines the only coniferous trees suitable for 

pruning in the Northeast, or is it feasible to prune red 

spruce as well? Although red spruce is an important lumber 

species in the spruce-fir region, it is seldom pruned because of its relatively slow rate of growth. 

In the winter of 1951, 127 red spruce and 46 eastern 

white pine trees were pruned on the Penobscot Experimental 

Forest near Bangor, I4aine.l White pine trees scattered 

throughout the spruce-fir stands afford an opportunity to 

compare the development of both species under similar conditions. (This report will discuss differences in growth by 

crown classification over the first 5 years after pruning.) 

The crop trees were selected for pruning on the basis 

of desirable vigor, form, crown class, crown ratio, and size 

and number of branches. With few exceptions, the trees were 

pruned to 18 feet to produce one clear 16-foot butt log 

above the stump. The red spruce trees averaged 6.1 inches 

1 and white pine 7.7 inches at time of pruning. 

Five growing seasons later, the spruce averaged 6.7 

inches and the white pine 8.7 inches, an average growth of 

0.65 and 1.0 inches respectively. White pine, which generally has larger limbs and slightly thicker bark than spruce, 

required an average of 1.3 inches of growth to cover the 

larger knots completely, as compared to 1 inch for red 

spruce. 

The 5-year growth of the pruned trees was analyzed to 

see if there was any correlation between growth and their 

crown class or crown ratio. T. F. ~c~intock~ found in an 

earlier study of unpruned trees that crown ratio and--to a 

lesser extent--crown class were good criteria for predicting 

growth of vigorous spruce. (crown ratio is the percent of 

the tree in living crown measured to the nearest 10 percent 

and expressed as a whole number.) 

In the present study, the 5-year results indicate 

that difference in growth between crown classes is not significant at the 5-percent level for pruned red spruce, but 

is highly significant for pruned white pine (table 1). HOWever, the growth rate of both pine and spruce increased significantly as crown ratios were increased. 

 he Penobscot Research Center, Northeastern Forest 

Experiment Station, and the Forestry Department, University 

of Maine, cooperated in this study. 

'unpublished paper, "A tree classification for red 

spruce and balsam fir", on file at the Penobscot Research 

Center, Bangor, Maine. 
Table 1.--Increment in relation to crown class and crown ratio 

Red spruce White pine 

Itear Average Average Trees increment Trees increment 

No. Inches No. Inches 

Crown class 

Dominant and codominant 60 0.680 29 1.131 

Intermediate 67 .615 17 .765 

Total, all trees 127 0.646 46 0.998 

Crown ratio 

4 25 0.500 14 0.764 

5 74 .638 22 1.009 

6 28 .796 10 1.290 

Total, all trees 127 0.646 4 6 0.998 

Unless trees grow reasonably fast, the cost of pruning plus interest to the end of the rotation will equal or 

exceed the increase in wood value resulting from the pruning. It is not known just how fast red spruce should grow 

in order to return a profit from pruning; no thorough economic study has been made. However, from general considerations of present lumber values, pruning costs, and other 

pertinent factors, it seems reasonable to assume that a diameter growth rate of at least 0.8 inch per 5-year period is 

necessary for pruning to show a return. 

Although average growth rates of both pine and spruce 

increased with increasing crown ratios, averages do not tell 

the whole story because they may include both fast- and 

slow-growing trees. Among the red spruce, there were 28 

trees with a crown ratio of 6; for these trees the average 

5-year growth was 0.8 inch (table l), but only 13 of them 

or 46 percent actually grew 0.8 inch or more. Of the 102 

trees with crown ratios of 5 or higher, only 37 (36 percent) 

grew 0.8 inch or more. Obviously, crown ratio in red 

spruce is not very reliable as a guide for selecting individual trees of faster growth rate. 

With white pine, the situation was quite different. 

Of the 29 dominants and codominants, 19 grew better than 1.0 

inch in the 5-year period. Half of the 12 intermediates 

with a crown ratio of 5 or more grew at least 1.0 inch. This 

indicates that practically any dominant or codominant pines, 

or intermediates with a crown ratio of 5 or greater, should 

be acceptable for pruning. 

The 5-year growth figures from this study show that 

pruned red spruce grew only two-thirds as fast as white 

pine. Nevertheless, some red spruce with long crowns do 

grow fast enough that they might profitably be pruned. The 

problem is to identify these fast-growing trees. Further 

study is necessary to find a more reliable indicator of 

rapid growth than crown length alone. 

--GRANT DAVIS, Research Forester 

Penobscot Research Center 

Northeastern Forest Experiment Station 

Forest Service, U.S. Dept. Agriculture 

Bangor, Maine 

2 AGRICULTURE-FOREST SERVICE-UPPER DARBY